Bornella anguilla, or "eel nudibranch.' This has been seen only once in Hawaiian waters. I had to travel to tiny Gato Island near Malapascua, Philippines to finally find it. It is named the eel nudibranch because of the way it swims, undulating sideways through the water.
Pteraeolidia ianthina, the "Blue Dragon Nudibranch" is a beautiful kind of sea slug. In the Philippines this species is a vivid purple color underwater.